PRESERVATIVE SYSTEM FOR CONTACT LENS SOLUTIONS

Abstract: A preservative system for ophthalmic solutions, particularly contact lens solutions, comprises: (a) chlorhexidine or a water-soluble salt thereof; and (b) polyhexamethylene biguanide or a water-soluble salt thereof.

Description: PRESERVATIVE SYSTEM FOR CONTACT LENS SOLUTIONS BACKGROUND OF THE INVENTION This invention relates to an improved preservative system for ophthalmic solutions, especially solutions for the care of contact lenses. The solutions contain as the preservative chlorhexidine and polyhexamethylene biguanide, or salts thereof. Since ophthalmic solutions, including solutions used for the care of contact lenses, either directly or indirectly come into contact with the eye, it is important that the solutions do not become contaminated with microorganisms. Conventionally, such solutions are packaged under sterile conditions, and many solutions incorporate an antimicrobial agent as a preservative for inhibiting growth of microorganisms which may contaminate the solution. For ophthalmic solutions used for contact lens care, the antimicrobial agent often also serves to disinfect and/or preserve contact lenses when rinsed or immersed in the solution. A challenge is to develop preservative systems which not only have a wide spectrum of antimicrobial activity but which also are more suitable for ophthalmic applications and less irritating to the eye. Preservatives provide desired antibacterial effects, but preservatives are, by their nature, irritating to the eye. Thus, while antimicrobial efficacy of a solution could be improved by merely increasing the amount of the active agent, the potential for eye irritation increases as the concentration of the active agent is increased. Conversely, decreasing the concentration of the antimicrobial agent could lessen eye irritation, but antimicrobial efficacy would decrease. SUMMARY OF THE INVENTION The present invention relates to improved ophthalmic solutions which comprise an antimicrobially effective amount of a preservative, wherein the preservative comprises: (a) chlorhexidine or a water- soluble salt thereof; and (b) polyhexamethylene biguanide or a water-soluble salt thereof. Additionally, the invention relates to methods of treating contact lenses, such as methods of disinfecting contact lenses, which employ an ophthalmic solution comprising the antimicrobial agent. DETAILED DESCRIPTION OF THE INVENTION The first component of the preservative system is a compound selected from the group consisting of chlorhexidine (1,1'-hexamethylene-bis[5-(p- chlorophenyl) biguanide]) and water soluble salts thereof. Suitable salts include the gluconate. isethionate (2-hydroxyethanesulfonate) , formate, acetate, glutamate, succinamate, monodiglycollate, dimethanesulfonate, lactate, diisobutyrate and glucoheptonanate salts. A preferred material is chlorhexidine gluconate (available from ICI Americas, Inc. , Wilmington, Delaware, USA) . The second component of the preservative system is a compound selected from the group consisting of polyhexamethylene biguanide (a polymer of hexamethylene biguanide, also referred to as polyaminopropyl biguanide) and water-soluble salts thereof. The polyhexamethylene biguanides include repeating units of the formula: -[-(CH 2 ) 3 -NH-C-NH-C-NH-(CH 2 ) 3 -] n - \\ II NH NH wherein n is 2 to 500, and include biguanides represented by formula (I) : NH 2 (CH 2 ) 3 "[-(CH 2 ) 3 -NHCNHCNH-(CH 2 ) 3 -] n -(CH 2 ) 3 -NH-C-NH-CN 11 H i| NH NH NH wherein n is 2 to 500, and water-soluble salts thereof. Preferred polyhexamethylene biguanides include lower molecular weight oligomers, including biguanides of formula (I) wherein n averages between 4 to 12. Suitable salts include the hydrochloride, borate, acetate, gluconate, sulfonate, tartrate and citrate salts. A more preferred material is the polyhexamethylene biguanide hydrochloride available under the trade name Cosmocil CQ (ICI Americas Inc., Wilmington, Delaware, USA) . Applicants have discovered that the preservative system of this invention provides desired antimicrobial efficacy with relatively low amounts of chlorhexidine and polyhexamethylene biguanide, thus reducing the potential for eye irritation from these preservatives. The preservative system is employed in ophthalmic solutions in an antimicrobially effective amount. As used herein, the term "ophthalmic solution" denotes an aqueous solution intended for application in the eye, including solutions for the care of contact lenses. Contact lens solutions include solutions for the care of soft hydrogel lenses and hard lenses including rigid gas permeable (RGP) lenses. Such solutions for the care of contact lenses include saline solutions, cleaning solutions, disinfection solutions, conditioning solutions, soaking solutions and rinsing solutions. The term "preservative" or "preservative system" denotes the agents included in the ophthalmic solutions for the purpose of inhibiting the growth of microorganisms in the product, thereby helping to maintain sterility during use. Additionally, the term "antimicrobial agent" is used herein to denote a specific active agent which provides the antimicrobial efficacy. The term "antimicrobially effective amount" denotes an amount which is effective to at least inhibit growth of microorganisms in the solution. Preferably, the amount of antimicrobial agents is sufficient to disinfect the solution by killing microorganisms therein according to international preservative efficacy requirements for ophthalmic solutions, including FDA and British Pharmacopeia requirements. Generally, the ophthalmic solutions include about 0.0005 to about 0.0060 weight percent of the chlorhexidine component, and about 0.00001 to about 0.0015 weight percent of the polyhexamethylene biguanide component. According to preferred embodiments, the ophthalmic solutions include no more than about 0.0040 weight percent of the chlorhexidine component, and no more than about 0.0010 weight percent of the polyhexamethylene biguanide, in order to minimize eye irritation; preferably, the solutions include at least about 0.0020 weight percent of the chlorhexidine component and at least about 0.0001 weight percent of the hexamethylene biguanide component, in order to ensure adequate antimicrobial efficacy. Although the optimum amounts of the antimicrobial agents may vary among specific ophthalmic solutions, specific amounts of each antimicrobial agent can be readily determined by a person of ordinary skill in the art following testing methods known in the art. The ophthalmic solutions may include other components known in the art. Preferably, the solutions further include a sequestering agent (or chelating agent) which is normally present at about 0.025 to about 2.0 weight percent. Examples of preferred sequestering agents include ethylenediaminetetraacetic acid (EDTA) and its salts, with the disodiu salt (disodiu edetate) being especially preferred. Generally, the solutions include buffering agents for buffering or adjusting pH of the solution, and/or tonicity adjusting agents for adjusting the tonicity of the solution. Representative buffering agents include: alkali metal salts such as potassium or sodium carbonates, acetates, borates, phosphates, citrates and hydroxides; and weak acids such as acetic, boric and phosphoric acids. Generally, buffering agents are present at about 0.01 to about 2.5 weight percent. Representative tonicity adjusting agents include: sodium and potassium chloride, and those materials listed as buffering agents. The tonicity agents may be employed in an amount effective to adjust the osmotic value of the final solution to more closely resemble that of human tears, generally at about 0.01 to about 2.5 weight percent. Additionally, the solutions may include wetting agents or viscosity modifiers. Representative wetting agents and viscosity modifiers include: cellulose derivatives, such as cationic cellulosic polymers, hydroxypropyl methylcellulose, hydroxyethylcellulose and methylcellulose; polyols, such as polyethylene glycol, glycerine and polyethylene oxide (PEO) containing polymers; polyvinyl alcohol; and polyvinyl pyrrolidone. Such additives may be used in a wide range of concentrations as is known in the art. The following examples further illustrate preferred embodiments of the present invention. EXAMPLE 1 Three contact lens solutions for conditioning and disinfecting contact lenses were prepared by mixing the components listed in Table 1. It is noted that Solution A includes the preservative system of this invention, whereas Solutions B and C were prepared for comparative purposes. TABLE I Component fWt. %) Soln A Soln B Soln C Chlorhexidine Gluconate 0.0030 0.0060 Polyhexamethylene Biguanide HCl 0.0005 0.0015 Disodium Edetate 0.050 0.050 0.050 Phosphate Buffer 0.335 0.335 0.335 Tonicity Adjusting Agents 0.950 1.000 0.950 Wetting Agents and/or Viscosity Modifiers 1.200 1.095 0.670 Purified Water q.s. q.s. q.s. to 100 to 100 to 100 Cosmocil CQ The contact lens solutions from Table I were subjected to challenge tests to determine efficacy against various organisms. Samples of each solution were inoculated with the organisms at the concentrations shown in Table II. Viability was tested at various periods following initial inoculation as reported in Tables III, IV and V. In the tables, "TNTC" designates "too numerous to count". TABLE II Organism Inoculum fcfu/ml) Staphylococcus aureuε 6538 1.6x10° adapted Serratia marceεcens 48 1.5X10 6 Serratia marcescens 48 2.1X10 6 Pesudomonas cepacia 25416 4.4X10 5 Aspergillus niger 2.5X10 5 Pseudomonas aeruginosa 9027 1.9X10 6 TABLE III Solution A Viability (cfu/ml) Organism 6Hr IDay 7Day 16Day 28Day S. aureus OxlO -1 OxlO J OxlO" OxlO- 1 - 0X10 J ad. S. marceεcenε OxlO 1 0x10^ oxio : OxlO 1 0xl0 S. marceεcenε OxlO 1 oxio- 1 - oxio- OxlO 1 0X10 ] P. cepacia 34X10 1 0x10 0x10" OxlO 1 0xl0 ] A. niger 98xl0 3 32x10 lxlO ] OxlO" 1 - OxlO" P. aeruginoεa OxlO 1 0x10 oxio " OxlO" OxlO" TABLE IV Solution B Viability fcfu/ml) TABLE V Solution C Viability (cfu/mlϊ Organism 6Hr IDav 7Day 16Day 28Day S. aureuε OxlO J 0xl0 J 0X10 1 OxlO 1 0 10^ ad. S. marceεcenε 0x10 0X10 J 0xl0 J 0xl0 J OxlO S. marceεcenε 0x10 0xl0 ] OxlO 1 0xl0 ] OxlO 1 P. cepacia 0x10 0xl0 ] oxio : 0X10 ] OxlO 1 A. niger 143x10 146x10" 95X10" 21x10- 4X10 3 P. aeruginoεa 0x10 OxlO 1 OxlO 1 OxlO 1 OxlO 1 EXAMPLE 2 Each of Solutions A, B and C from Example 1 was subjected to the following experiments to determine potential eye irritation of the solutions. The experimental methods follow the procedure developed by R. Tchao, which is described in "Trans-Epithelial Permeability of Fluorescein In Vitro as an Assay to Determine Eye Irritants", Progress in In Vitro Toxicology, Volume 6, 1988, pages 271-283 (Mary ann Liebert, Inc. Publishers, New York) , the disclosure of which is incorporated herein by reference. The Tchao technique is described as a method of determining potential eye irritation of a substance by correlating damage to a monolayer of Madin-Darby Canine Kidney (MDCK) cells with damage to corneal epithelial cells. Monolayer cultures of MDCK cells were grown on a filter membrane. The growth medium was removed and the cells were rinsed with Hanks Balanced Salt Solution (HBSS) . Aliquots of Solutions A, B and C were applied to the obtained cell onolayers, incubated for 60 minutes, and then the test samples were removed and the cells were rinsed with HBSS. As a control, HBSS was applied to a cell monolayer in place of the test solutions. A sodium fluorescein solution was then applied to each cell monolayer for 30 minutes. Subsequently, the amount of fluorescein passing through the monolayer is quantified by fluorescence spectroscopy. The results are summarized in Table VI. The amount of fluorescein passing through the cell monolayer is a function of permeability of the cell monolayer. Higher cell monolayer permeability indicates greater damage to the cell junctions from application of a test solution thereto, whereas lower cell monolayer permeability indicates less severe damage to the cell junctions from application of the test solution. TABLE VI Test sam le Fluorescence units Control 55 (± 7) Solution A 67 (+ 12) Solution B 73 (+ 1) Solution C 134 (± 11) The data summarized in Tables III, IV and V demonstrates that the solution of this invention (Solution A) provided a broader spectrum of antimicrobial efficacy than either of the comparative formulations (Solutions B and C) . Additionally, the improved efficacy was achieved despite using lower amounts of the individual agents, i.e., the subject solution contained 0.0030 weight % chlorhexidine gluconate versus 0.0060 weight % chlorhexidine gluconate in Solution B, and 0.0005 weight % polyhexamethylene biguanide versus 0.0015 weight % polyhexamethylene biguanide in Solution C. The improved efficacy for Solution A was especially significant when compared with Solution B. While the improvement in efficacy was less significant when compared with Solution C, the data summarized in Table VI demonstrates that Solution A exhibited significantly less potential for eye irritation than Solution C. EXAMPLE 3 Various preservative systems were employed in saline solution buffered with a phosphate buffer. The resultant six solutions contained the antimicrobial agents shown in Table VII, noting that various solutions also contained disodium edetate as a sequestering agent. Each of the six solutions was subjected to challenge tests, wherein samples of each solution were inoculated with the organisms at the concentrations shown in Table VIII. Viability was tested at various periods following initial inoculation as reported in Tables IX, X, XI, XII, XIII and XIV. TABLE VII Solution Component _E F G H CHG" (Wt. %) 0.0030 0.0030 0.0030 0.0030 PHMB HC1 (Wt. %) 0.0005 0.0005 0.0005 — 0.0005 *** Na 2 EDTA (Wt. %) 0.050 0.050 0.050 ** Chlorhexidine Gluconate Polyhexamethylene Biguanide Hydrochloride (Cosmocil CQ) Disodium Edetate TABLE VIII Organism Inoculum fcfu/ml) Pεeudomonaε aeruginoεa 9027 3.9x10* Staphylococcuε aureuε 6538 1.4x10* Aspergilluε niger 2.9xlO J Candida albicanε 6.0xlO J adapted Serratia marceεcenε 48 3.8x10* Serratia marceεcenε 48 2.4x10* TABLE IX Solution D V-iabnitv refu/ml. Orσanisni 6Hr iDa 2Dav 7Dav 14Dav 2iPay 2?Pay OxlO 1 OxlO 1 0X10 J OxlO J 254X10 3 192X10 3 OxlO 1 OxlO 1 0X10 J Oxl0 ad ε. marceεcenε 170xlO α 19X10 1 lxlO 1 OxlO 1 468X10 1 3X10 1 27X10 1 TABLE X Solution E Viability _cfu/ml_ Orσan ism βHr IDa 2Dav 7paγ 14Paγ 21Dav 28Dav P. aerugiosa OxlO- 1 OxlO" 1 OxlO J OxlO 0X10 J 0X10 OxlO J ε. aureuε 95X10 3 4X10 3 OxlO 3 0X10 OxlO3 33 OxlO ) 33 OxlO 3 A. niger 72xl0 3 168X10 3 87X10 3 9X10 ixio .. J . 0X10 .1 J 2X10 3 C. albicanε 4X10 J 1X10 OxlO 3 0x10 OxlO 3 OxlO 3 OxlO 3 ε. marceεcenε 12X10 3 OxlO 3 OxlO 3 0x10 OxlO 1 OxlO 1 OxlO 1 ad ε. marceεcenε 624xlθ 3 57xl0 3 4xl0 3 OxlO Oxl0 J OxlO J OxlO J TABLE XI Solution F Viability .cfu/al. Organism J5Hϊ_ IDav 2Dav 7Dav 14Paγ 21Dav 28Dav P. aerugiosa OxlO -1 OxlO- 1 OxlO -1 OxlO OxlO J Oxl0 J OxlO J ε. aureuε OxlO 1 OxlO 1 OxlO 1 OxlO 3 OxlO 3 OxlO 3 O lO 3 A. niger 213X10 3 227X10 3 126X10 3 134xl0 ; 3X10 3 2X10 3 lxlO 3 C. albicanε lxlO 1 OxlO 1 OxlO 1 OxlO 3 O lO 3 OxlO 3 OXlO 3 ε. marceεcenε OxlO 1 OxlO 1 OxlO 1 OxlO 3 OxlO 3 OxlO 3 OxlO 3 ad 5. marceεcenε 62X10 1 OxlO 1 OxlO 1 OxlO 3 OxlO 3 OxlO 3 OXlO 3 TABLE XII Solution G Viabil ity fefu/ml . Organism 6Hr IPpy 2Dav 7Dav 14 BY LΩOX. ZSΣax P. aerugiosa oxio- 1 oxio A oxio- * - OxlO A OxlO J 0X10 1 OxlO 1 S. aureuε ft0vX1.n0 * * ΛOxl.nOl x Λoxuiinol- 1 OxlO x oxio- 1 OxlO x A. niger 250X10 3 266X10 3 184X10 3 136X10 3 126X10 3 131X10 3 221X10 3 c. albicanε OXlO J OxlO 0X10 J OXlO J 0X10 J OX10 J OxlO S. marceεcenε OXIO 3 lxlO 3 oxio 3 oxio 3 OxlO 3 oxio 3 oxio 3 ad ε. marceεcens 700X10 1 lOxlO 1 22X10 1 OxlO 1 OxlO 1 OxlO 3 OxlO 3 TABLE XIII Solution H Viability fefu/ml. Organism 6Hr Dav 2Dav 7PPY 14P9Y 21Dav 28Dav P. aerugiosa OxlO J OxlO J 0X10 J OXIO 1 OXIO 1 OxlO 0X10 5. aureuε 258X10 3 OxlO 3 OXIO 3 0X10 J OxlO J 0X10 0X10 A. niger 134X10 3 144X10 3 122X10 3 18X10 3 3X10 3 0X10 0X10 c. albicanε 181X10- 10XlO J 5X10- 1 OXIO 3 OXIO 3 OxlO 0X10 ε. marceεcenε 2X10 3 OXIO 3 OXIO 1 OxlO 3 OxlO 3 0X10 OxlO ad ε. marceεcenε 64OxlO 3 TNTC TNTC TNTC TNTC 78X10 1 OxlO 1 TABLE XIV Solution J Viability fefu/ml. Organism 6Hr 1PPY 2PBY 7Dav 14Dav 21Dav 28Dav P. aerugiosa OxlO x 0X10 J OxlO A oxio- 1 Oxl0 0X10 0X10 J ε. aureuε OX10 J 0X10 oxio 1 oxio 3 O IO 3 0X10 OxlO 3 A. niger 78X10 3 150X10 3 191X10 3 13X10 3 4X10 3 2X10 OXIO 3 C. albicanε 1X10 1 OXIO 1 OxlO 1 OXIO 3 O IO 3 OxlO oxio 3 S. marceεcenε OXIO 4 0X10 OxlO 1 OXIO 3 OxlO 3 0X10 OxlO 3 ad S. aarcescenε 35X10 3 0X10 O IO 1 OxlO 3 oxio 3 0X10 OxlO 3 — I D" Although certain preferred embodiments have been described, it is understood that the invention is not limited thereto and modifications and variations would be evident to a person of ordinary skill in the art. We claim:

Claims: CLAIMS: 1. An ophthalmic solution comprising an antimicrobially effective amount of a preservative, wherein the preservative comprises: (a) chlorhexidine or a water-soluble salt thereof; and (b) polyhexamethylene biguanide or a water-soluble salt thereof. 2. The solution of claim 1, wherein component (a) is a water-soluble salt of chlorhexidine. 3. The solution of claim 2, wherein component (a) is chlorhexidine gluconate. 4. The solution of claim 1, wherein component (b) is a water-soluble salt of polyhexamethylene biguanide. 5. The solution of claim 4, wherein component (b) is polyhexamethylene biguanide hydrochloride. 6. The solution of claim 3, wherein component (b) is polyhexamethylene biguanide hydrochloride. 7. An aqueous solution for treating contact lenses comprising: (a) about 0.0005 to about 0.0060 weight percent of chlorhexidine or a water-soluble salt thereof; and (b) about 0.00001 to about 0.0015 to weight percent of polyhexamethylene biguanide or a water- soluble salt thereof. 8. The solution of claim 7, wherein component (a) is chlorhexidine gluconate and component (b) is hexamethylene biguanide hydrochloride. 9. The solution of claim 7, wherein component (a) is present at about 0.0020 to about 0.0040 weight percent and component (b) is present at about 0.0001 to about 0.0010 weight percent. 10. The solution of claim 9, wherein component (a) is present at about 0.0030 weight percent and component (b) is present at about 0.0005 weight percent. 11. The solution of claim 7, further comprising about 0.01 to about 2.5 weight percent of at least one buffering agent. 12. The solution of claim 7, further comprising about 0.025 to about 2.0 weight percent of ethylenediaminetetraacetic acid or a salt thereof. 13. The solution of claim 12, further comprising about 0.025 to about 2.0 weight percent of sodium edetate. 14. The solution of claim 7, further comprising at least one viscosity modifier. 15. The solution of claim 7, further comprising at least one wetting agent. 16. A method of treating a contact lens which comprises treating the lens with an aqueous solution comprising an antimicrobially effective amount of: (a) chlorhexidine or a water-soluble salt thereof; and (b) polyhexamethylene biguanide or a water- soluble salt thereof. 17. The method of claim 16, wherein component (a) is a water-soluble salt of chlorhexidine and component (b) is a water-soluble salt of polyhexamethylene biguanide. 18. The method of claim 17, wherein component (a) is chlorhexidine gluconate and component (b) is polyhexamethylene biguanide hydrochloride. 19. The method of claim 14, wherein the solution comprises: (a) about 0.0005 to about 0.0060 weight percent of chlorhexidine or a water-soluble salt thereof; and (b) about 0.00001 to about 0.0015 to weight percent of polyhexamethylene biguanide or a water- soluble salt thereof. 20. The method of claim 19, wherein component (a) is present at about 0.0020 to about 0.0040 weight percent and component (b) is present at about 0.0001 to about 0.0010 weight percent. 21. A method of preserving an ophthalmic solution which comprises including in the solution an antimicrobially effective amount of a preservative system consisting essentially of: (a) chlorhexidine gluconate; and (b) polyhexamethylene biguanide hydrochloride. 22. The method of claim 21, wherein the solution includes disodium edetate.

Inventors: RAHEJA MANOHAR K, WROBEL STANLEY J, RAHEJA, MANOHAR, K., WROBEL, STANLEY, J.
Applicants: POLYMER TECHNOLOGY CORP, POLYMER TECHNOLOGY CORPORATION
Application year: 1994
Main classification: A61L2
IPC codes: A01N47, A61K9, A61L2, A61L12, G02C13